Hepatic Glycogen Synthesis in Adrenalectomized Rats After Short- and Longterm Stimulation by Dexamethasone Observed by Light and Electron Microscopic Radioautography
The effects on glycogen synthesis of short- and long-term stimulation with dexamethasone (DEX) were studied in adrenalectomized, overnight-fasted rats by light (LM) and electron microscopic (EM) radioautography (RAG). Rats were injected with DEX 3 hr (short-term) or 14 hr (long-term) prior to labeling by intravenous injection of 2 mCi 3H-galactose, a glycogen precursor. Liver was prepared for LM and EM RAG by routine procedures.Short-term rats were sacrificed 1, 6 and 12 hr after labeling. One hr after injection of label (Fig. 1) equal percentages (44%) of heavily (> 10 grains/100 μm2 hepatocyte cytoplasm) and lightly (<10 grains/100 μm2 cytoplasm) labeled hepatocytes were evident. Six hr after labeling, heavily labeled cells increased slightly as labeled and unlabeled glycogen became evident. The appearance of unlabeled glycogen was evidence that glycogen synthesis continued between 1 and 6 hr, as circulating label fell to a level below that necessary for radioautographic labeling to occur. Twelve hr after labeling (Fig. 2) the percentage of heavily labeled hepatocytes (31%) decreased to less than at one hour as unlabeled glycogen increased. These results indicated that although glycogen synthesis had continued, some loss of label had occurred.